It is known in the prior art to measure the acceleration of an object using an accelerometer. When a user taps an object, the object undergoes a rapid acceleration. A tap is simply a synonym for a light strike, pat or rap that causes an object to undergo acceleration. This acceleration can be measured and compared to a threshold in order to identify when a tap has occurred. The accelerometer threshold is set both in a positive and a negative direction and there may be separate thresholds for each of the cardinal directions. If the acceleration is greater than the threshold a tap is identified. As shown in the exemplary graph of FIG. 1, five taps are recognized using this acceleration and threshold technique. One tap can be identified by a strong negative acceleration 110, one with a strong positive acceleration 120 and three that just reach the threshold 130, 140, 160. Other points in the acceleration vs. time plot that are circled 150, 170, and 180 show changes in the acceleration that are actually taps, however the values do not reach the threshold and therefore are not registered as taps. Additionally, the prior art methodology even registers a tap 160 when no tap occurs.
Although the threshold can be adjusted so as to better identify when taps occur, moving the threshold will also lead to an increase in false-positive tap identifications. If this methodology is employed in a cellular phone or other personal electronic device, such false-positives will cause the device to activate a function even when the operator does not wish to have the device activated. For, example if a cellular phone is in the pocket of a user and the user moves, the cellular phone may accelerate or come into contact with an object in the user's pocket unintentionally activating the tap feature. Noise both internal and external can cause the accelerometer to register a value that is above the threshold thereby recording a false-positive.
If the threshold is set too high in order to avoid false-positives, user's will become frustrated with the tap activation feature, since the user's taps will not be recognized and the device will not perform the function that the user desires. As a result of this frustration, the user will disable the tap feature.